In wireless communication systems, multi-path fading may be described as very quick fading conditions that may cause bit errors leading which might lead to discarded frames/packet drop. For highly loss sensitive data such as for example High Definition Television (HDTV) streams etc., this may cause very noticeable service degradation for the end user. Fading is related to attenuation of the signal. Examples of different types of fading may be:                1. Rain fading (fairly slow attenuation envelope).        2. Defocusing and ducting (long events, fairly fast envelope).        3. Multi-path propagation fading (very fast envelope and quick events).        
Protection against multi-path fading is most often performed by using two different antennas mounted a distance apart, e.g. a few meters apart. If the calculation of the distance between the two antennas has been performed correctly, at least one of the antennas will have a good signal during multi-path fading conditions.
For Plesiosynchronous Digital Hierarchy (PDH)/Time Division Multiplexing (TDM) based traffic, protection against multi-path fading has traditionally been performed by configuring the radios attached to the antennas in 1+1 configuration (two transmitters sending the same data) with one receiver active and the other passive and the receiver switched channel depending on which radio who had the best signal quality.
When native packet based data was introduced in the microwave radio link domain, it became possible to perform a layer one (L1) segmentation of the data stream to provide 2+0 protection schemes, or n+0, in case of more radios. A 2+0 protection scheme implies that there are two active transmitters. In case one of the received data streams have errors (link goes down), the capacity will be reduced by one link. This configuration provided at least twice the bandwidth utilization, since the data did not have to be sent on both channels simultaneously.
In case of multi-path fading scenarios, one of the radios channels in the 2+0 pair will start to receive bit errors due to fading. Since data is shared over the two links instead of being duplicated (as for 1+1), packet drop that is not control by Quality of Service (QoS) mechanisms will occur.
Existing QoS mechanisms may provide quality feedback to the transmitter. Quality feedback may be provided in several ways, for example in case that the radio support the feature Automatic Transmission Power Control (ATPC), the receiver will continuously be provided with information of the signal strength from the corresponding receiver on the other side of the hop. Another example may be in case that the radio supports adaptive modulation, where quality information is sent from the receiver on the other side of the hop to the transmitting modem in order to adjust its modulation scheme according to the received signal quality.
The existing solutions have several drawbacks:    1+1: Poor bandwidth utilization (50%). Good protection of high priority data.    2+0: Good bandwidth utilization (up to 100%), but poor protection of high priority data against multi-path fading.    1+½+0: Good bandwidth utilization for low priority data (100%), poor utilization for high priority data (50%), but good protection against packet drop of high priority data during multi-path fading.